Three-dimensional steering tool for controlled downhole extended-reach directional drilling

ABSTRACT

A steering tool for extended-reach directional drilling in three dimensions comprises a mud pulse telemetry section, a rotary section, and a flex section assembled as an integrated system in series along the length of the tool. The flex section comprises a flexible drive shaft and a deflection actuator for applying hydraulic pressure along the length of the shaft for bending the shaft when making inclination angle adjustments during steering. The rotary section comprises a rotator housing coupled to the deflection housing for rotating the deflection housing for making azimuth angle adjustments during steering. The onboard mud pulse telemetry section receives inclination and azimuth angle steering commands together with actual inclination and azimuth angle feedback signals during steering for use in controlling operation of the flex section and rotary section for steering the tool along a desired course. The steering tool can change inclination and azimuth angles either simultaneously or incrementally while rotary drilling.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a division of application No. 10/282,481,filed Oct. 28, 2002, which is a continuation of application No.09/549,326, filed Apr. 13, 2000, now U.S. Pat. No. 6,470,974, whichclaims the priority of provisional application No. 60/129,194, filedApr. 14, 1999, the entire disclosure of which is incorporated herein byreference.

FIELD OF THE INVENTION

[0002] This invention relates to the drilling of boreholes inunderground formations, and more particularly, to a three-dimensionalsteering tool that improves extended reach directional drilling ofboreholes.

BACKGROUND OF THE INVENTION

[0003] There is a need for drilling multiple angled, long reachboreholes from a fixed location such as from an offshore drillingplatform. Historically, several methods have been used to change thedirection of a borehole. With the requirement for multiple extendedreach drilling of wells from offshore platforms came the need for ameans for steering the drilling assembly more accurately. In the 1970s,the downhole motor and Measurement-While-Drilling (MWD) with a bent subwere introduced. Steering was accomplished by stopping rotary drillingand installing the downhole motor-bent sub assembly and an orientationtool. After making a trip into the borehole, the orienting tool wasactuated and locked into the desired tool face angle—the angle of theassembly at the bottom of the hole similar to the points of a compass.The downhole motor's bent sub (typically with a two-degree bend) isactuated by increasing pump pressure, thus turning the motor and thedrill bit. The assembly drills ahead with the drill string slidingforward and only the drill bit rotating, thus increasing the hole buildangle approximately 2 degrees per length of the motor until the desiredangle is achieved. It is during the sliding advancement of the drillstring that differential sticking (a significant and frequently incurredproblem) is most prevalent. The downhole motor is retrieved, thusrequiring another trip to the surface. In later designs, after drillingthe build section and when a short straight hole section is required, atrip to the surface can be delayed by rotating the bent sub downholemotor at drilling speeds (5-150 RPM) until the short straight section isdrilled. This method can drill an approximately straight but slightlyenlarged hole for short distances. The amount of time between trips istypically limited by the life of the downhole motor (80-100 hours),rather than the life of the bit (the preferred condition) which can beas high as 350-400 hours.

[0004] Thus, drilling with a downhole motor and a bent sub hasdisadvantages of being expensive and time consuming because of the tripsin and out of the borehole when steering to each desired new angle, andthis approach is unreliable because the downhole motor has a greatertendency to break down under these conditions.

[0005] Later, steering tools that were directly attached to the drillstring were developed. Modern steering tools of this type are eitherdiscrete or integrated. Discrete steering tools include Halliburton'sTRACS 2D, Maersk's “wall grabber” style tool, Directional DrillingDynamics' tool that rotates through a bend, and the Cambridge Radiationtool that includes a non-rotating body that deflects the drill string.

[0006] Integrated steering tools are part of an assembly of otherdownhole tools including downhole sensors. Suppliers of these includeHalliburton's TRACS 2D, Smith Red Barron which includes a non-rotatingnear bit stabilizer (Wall Grabber), and the ANADRILL tool that is beingintegrated into a Camco tool. Baker Hughes Inteq has the AUTO TRAK toolthat includes directional resistivity and vibration measurements. Camcohas a 3-D SRD tool with sensors that can perform five jobs without amajor overhaul.

[0007] Certain prior art steering tools can change azimuth andinclination simultaneously. These tools, one of which is manufactured bySchlumberger, utilizes three pistons which extend laterally outwardlyfrom the drill string at different distances to push the drill stringoff center to change orientation of the drill string. This approachavoids use of a bent sub. However, use of pistons in a small diameterdrill hole to make steering adjustments is not desirable; and they arecostly and less reliable because of the large number of mechanicalparts.

[0008] The previously mentioned MWD system is a separate stand-aloneassembly comprising survey equipment which uses an inclinometer oraccelerometer for measuring inclination and a magnetometer for measuringazimuth angle. Inclination angle is typically measured away fromvertical (90 degrees from the horizontal plane), and azimuth angle ismeasured as a rotational angle in a horizontal plane, with magneticNorth at zero degrees and West at 270 degrees, for example.

[0009] There is a need for a low cost, highly reliable, long lifethree-dimensional rotary drilling tool that provides steering in bothazimuth and inclination while drilling. It is also desirable to providea steering tool which can change both inclination and azimuth angleswithout use of a downhole motor and bent sub and the time consuming andexpensive trips to the surface for changing orientation of the steeringtool. It would also be desirable to avoid use of wall grabber typesystems that require contact with the wall of the borehole to push thedrill string off center in order to change drilling angles.

[0010] The present invention provides a steering tool which can changeinclination and azimuth angles either continuously (simultaneously) orincrementally while rotary drilling and while making such steeringadjustments in three dimensions. Changes in inclination and azimuthwhile rotary drilling can be made with drilling fluid flowing throughthe drill string and up the bore. The steering assembly of thisinvention can respond to electrical signals via onboard mud pulsetelemetry to control the relative azimuth and inclination anglesthroughout the drilling process. Such three dimensional steering can beachieved without stopping the drilling process, without use of adownhole motor or bent sub, and without borehole wall contacting devicesthat externally push the drill string toward a desired orientation. Theinvention provides a steering tool having lower cost, greaterreliability, and longer life than the steering tools of the prior art,combined with the ability to improve upon long reach angular drilling inthree dimensions with reduced torque and drag.

SUMMARY OF THE INVENTION

[0011] Briefly, one embodiment of the invention comprises athree-dimensional steering tool for use in drilling a borehole in anunderground formation in which an elongated conduit extends from thesurface through the borehole and in which the steering tool is mountedon the conduit near a drill bit for drilling the borehole. The steeringtool comprises an integrated telemetry section, rotary section and flexsection. The steering tool includes an elongated drive shaft coupledbetween the conduit and the drill bit. The flex section includes adeflection actuator for applying a lateral bending force to the driveshaft for making inclination angle adjustments at the drill bit. Therotary section includes a rotator actuator for applying a rotationalforce transmitted to the drive shaft for making azimuth angleadjustments at the drill bit. The telemetry section measures inclinationangle and azimuth angle during drilling and compares them with desiredinclination and azimuth angle information, respectively, to producecontrol signals for operating the deflection actuator to make steeringadjustments in inclination angle and for operating the rotator actuatorfor making steering adjustments in azimuth angle.

[0012] In another embodiment of the invention, the flex section includesan elongated drive shaft coupled to the drill bit, and a deflectionactuator for hydraulically applying a lateral bending force lengthwisealong the drive shaft for making changes in the inclination angle of thedrive shaft which is transmitted to the drill bit as an inclinationangle steering adjustment. The rotary section is coupled to the driveshaft and includes a rotator housing for transmitting a rotational forceto the drive shaft to change the inclination angle of the drive shaftwhich is transmitted to the drill bit as an azimuth angle steeringadjustment. The telemetry section includes sensors for measuring theinclination angle and azimuth angle of the steering tool while drilling.Command signals proportional to the desired inclination angle andazimuth angle of the steering tool are fed to a feedback loop forprocessing measured and desired inclination angle and azimuth angle datafor controlling operation of the deflection actuator for makinginclination angle steering adjustments and for controlling operation ofthe rotator actuator for making azimuth angle steering adjustments.

[0013] In an embodiment of the invention directed to rotary drillingapplications, a rotary drill string extends from the surface through theborehole, and the steering tool is coupled between the rotary drillstring and a drill bit at the end for drilling the borehole. Thesteering tool includes an elongated drive shaft coupled between thedrill string and the drill bit for rotating with rotation of the drillstring when drilling the borehole. The flex section comprises adeflection actuator which includes a deflection housing surrounding thedrive shaft and an elongated deflection piston movable in the deflectionhousing for applying a lateral bending force lengthwise along the driveshaft during rotation of the drill string for changing the inclinationangle of the drive shaft to thereby make inclination angle steeringadjustments at the drill bit. The rotary section includes a rotatorhousing surrounding the drive shaft and coupled to the deflectionhousing. A rotator piston contained in the rotator housing applies arotational force to the deflection housing to change the azimuth angleof the drive shaft during rotation of the drill string to thereby makeazimuth angle steering adjustments at the drill bit. The telemetrysection measures present inclination angle and azimuth angle duringdrilling and compares it with desired inclination and azimuth angleinformation to produce control signals for operating the deflectionpiston and the rotator piston to make steering adjustments in threedimensions.

[0014] The description to follow discloses an embodiment of thetelemetry section in the form of a closed loop feedback control system.One embodiment of the telemetry section is hydraulically open loop andelectrically closed loop although other techniques can be used forautomatically controlling inclination and azimuth steering adjustments.

[0015] Although the description to follow focuses on an embodiment inwhich the steering tool is used in rotary drilling applications, theinvention can be used with both rotary and coiled tubing applications.With coiled tubing a downhole mud motor precedes the steering tool forrotating the drill bit and for producing rotational adjustments whenchanging azimuth angle, for example.

[0016] In one embodiment in which inclination and azimuth angle changesare made simultaneously, the steering tool can include a packerfoot(gripper) for contacting the wall of the borehole to produce a reactionpoint for reacting against the internal friction of the steering tool,not the rotational torque of the drill string.

[0017] These and other aspects of the invention will be more fullyunderstood by referring to the following detailed description and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is an elevational view showing the three dimensionalsteering tool of this invention.

[0019]FIG. 2 is a view of the three dimensional steering tool similar toFIG. 1, but showing the steering tool in cross-section.

[0020]FIG. 3 is a schematic functional block diagram illustratingelectrical and hydraulic components of the integrated control system forthe steering tool.

[0021]FIG. 4 is a functional block diagram showing the electroniccomponents of an integrated inclination and azimuth control system forthe steering tool.

[0022]FIG. 5 is a perspective view showing a flex shaft component of thesteering tool.

[0023]FIG. 6 is a cross-sectional view of the flex shaft shown in FIG.5.

[0024]FIG. 7 is an exploded view shown in perspective to illustratevarious components of a flex section of the steering tool.

[0025]FIG. 8 is a cross-sectional view of the flex section of thesteering tool in which the various components are assembled.

[0026]FIG. 9 is a fragmentary cross-sectional view showing a bearingarrangement at the forward end of the flex shaft component of the flexsection.

[0027]FIG. 10 is a fragmentary cross-sectional view showing a bearingarrangement at the aft end of the flex shaft component of the flexsection.

[0028]FIG. 11 is an elevational view showing a rotary section of thesteering tool.

[0029]FIG. 12 is a cross-sectional view similar to FIG. 11 and showingthe rotary section.

[0030]FIG. 13 is an enlarged fragmentary cross-sectional view takenwithin the circle 13-13 of FIG. 13.

[0031]FIG. 14 is an enlarged fragmentary cross-sectional view takenwithin the circle 14-14 of FIG. 12.

[0032]FIG. 15 is an enlarged fragmentary cross-sectional view takenwithin the circle 15-15 of FIG. 12.

[0033]FIG. 16 is an enlarged fragmentary cross-sectional view takenwithin the circle 16-16 of FIG. 12.

[0034]FIG. 17 is an exploded perspective view illustrating internalcomponents of an onboard telemetry section, flex section and rotarysection of the steering tool.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Referring to FIGS. 1 and 2, an integrated three dimensionalsteering tool 20 comprises a mud pulse telemetry section 22, a rotarysection 24, and an inclination or flex section 26 connected to eachother in that order in series along the length of the tool. The steeringtool is referred to as an “integrated” tool in the sense that the flexsection and rotary section of the tool, for making inclination angle andazimuth angle adjustments while drilling, are assembled on the sametool, along with a steering control section (the mud pulse telemetrysection) which produces continuous measurements of inclination andazimuth angles while drilling and uses that information to controlsteering along a desired course. A drill bit 28 is connected to theforward end of the flex section. A coupling 30 at the aft end of thetool is coupled to an elongated drill string (not shown) comprisingsections of drill pipe connected together and extending through theborehole to the surface in the well known manner. The inclination orflex section 26 provides inclination angle adjustments for the steeringtool. The rotary section 24 provides azimuth orientation adjustments tothe tool. The mud pulse telemetry section 22 provides command,communications, and control to the tool to/from the surface. The entiretool has an internal drilling bore 32, shown in FIG. 2, which allowsdrilling fluid (also referred to as “drilling mud” or “mud”) to flowthrough the tool, through the drill bit, and up the annulus between thetool and the inside wall of the borehole. In the embodiment illustratedin FIGS. 1 and 2, a 6.5 inch diameter tool is used in an 8.5 inchdiameter hole, and the tool is 224 inches long. Three dimensionalsteering is powered by differential pressure of the drilling fluid thatis taken from the drill string bore and discharged into the annulus. Asmall portion (approximately 5% or less of the bore flow rate) is usedto power the tool and is then discharged into the annulus.

[0036] The steering tool is controlled by the mud pulse telemetrysection 22 and related surface equipment. The mud pulse telemetrysection at the surface includes a transmitter and receiver, electronicamplification, software for pulse discrimination and transmission,displays, diagnostics, printout, control of downhole hardware, powersupply and a PC computer. Within the tool are a receiver andtransmitter, mud pulser, power supply (battery), discriminationelectronics and internal software. Control signals are sent from the mudpulse telemetry section to operate onboard electric motors that controlvalves that power the rotary section 24 and the inclination or flexsection 26. The steering tool is equipped with standard tool jointthreaded connections to allow easy connection to conventional downholeequipment such as the drill bit 28 or drill collars.

[0037]FIG. 3 is a schematic functional block diagram illustrating oneembodiment of an electro-hydraulic system for controlling operation ofthe flex section 26 and the rotary section 24 of the steering tool.Differential pressure of the drilling fluid between the drill stringbore and the returning annulus is used to power the rotary and flexsections of the three-dimensional steering tool. This drilling fluid isbrought into the drilling fluid control system from the annulus througha filter 34 and is then split to send the hydraulic fluid under pressureto the flex section 26 through an input line 36 and to the rotarysection 24 through an input line 38. Drilling fluid from the flexsection input line 36 enters an inlet side of a motorized flex sectionvalve 40, preferably a three port/two position drilling fluid valve.When the flex section is operated to change the inclination angle of thesteering tool the valve 40 opens to pass the drilling fluid to adeflection housing 42 schematically illustrated in FIG. 3. Thedeflection housing contains a flex shaft 44 which functions like asingle-acting piston 46 with a return spring 48 as schematicallyillustrated. Drilling fluid passes through a line 50 from the inlet sideof the valve 40 to a side of the deflection housing which applies fluidpressure to the piston section of the flex shaft for making adjustmentsin the inclination angle of the steering tool. After the tool hasachieved the desired inclination, the flex section valve is shifted toallow drilling fluid to pass through a discharge section of the valveand drain to the annulus through a discharge line 52. Flex piston travelis measured by a position transducer 54 that produces instantaneousposition measurements proportional to piston travel. These positionmeasurements from the transducer are generated as a position feedbacksignal for use in a closed loop feedback control system (describedbelow) for producing desired inclination angle adjustments duringoperation of the steering tool. The feedback loop from the flex positiontransducer to the flex valve's motor either maintains or modifies thevalve position, thus maintaining or modifying the inclination angle ofthe tool.

[0038] For the rotary section, the drilling fluid in the input line 38enters the inlet side of a rotary control valve 56, preferably a threeposition, four port drilling fluid valve. When the rotary section isoperated to produce rotation of the steering tool, for adjustments inazimuth angle, the control valve 56 opens to pass drilling fluid througha line 58 to a rotator piston 60 schematically illustrated in FIG. 3.The rotator piston functions like a double-acting piston; it moveslinearly but is engaged with helical gears to produce rotation of thedeflection housing containing the flex piston. Drilling fluid enters therotator piston which travels on splines to prevent the piston'srotation. The piston drives splines that rotate the deflection housing42 and thus, the orientation of the flex shaft, which causes changes inthe azimuth angle of the steering tool. Drilling fluid from the rotatorpiston is re-circulated back to the rotary section valve 56 through areturn line 61. Piston travel of the rotator piston is measured by arotary position transducer 62 that produces a position signal measuringthe instantaneous position of the rotator piston. The rotary positionsignal is provided as a position feedback signal in a closed loopfeedback control system described below. The feedback signal isproportional to the amount of travel of the rotator piston for use inproducing desired rotation of the steering tool for making azimuth angleadjustments. After the steering tool has achieved the desired azimuthadjustment, the rotary section valve is shifted to allow the fluid todrain through a discharge line 64 to the annulus.

[0039]FIG. 4 is a functional block diagram illustrating the electroniccontrols for operating the flex section and the rotary section of thesteering tool. The control system is divided into three major sections—amud pulse telemetry section 70, a feedback control loop 72 for the flexsection of the steering tool, and a feedback control loop 74 for therotator section of the tool.

[0040] The mud pulse telemetry section 70 includes surface hardware andsoftware 76, a transmitter and receiver 78, an actuator controller 80, apower supply (battery or turbine generator) 82, and survey electronicswith software 84. The survey equipment uses a inclinometer oraccelerometer for measuring inclination angle and a magnetometer formeasuring azimuth angle. The mud pulse telemetry receives inclinationand azimuth data periodically, and the controller translates thisinformation to digital signals which are then sent to the transmitterwhich comprises a mud pulse device which exhausts mud pressure into theannulus and to the surface. Standpipe pressure variations are measured(with a pressure transducer) and computer software is used to produceinput signal information proportional to desired inclination and azimuthangles. The position of the tool is measured in three dimensions whichincludes inclination angles (tool face orientation and inclination) andazimuth angle. Tool depth is also measured and fed to the controller toproduce the desired inclination and azimuth angle input data.

[0041] The mud pulse telemetry section includes 3-D steering toolcontrol electronics 86 which receive data inputs 88 from the surveyelectronics 84 to produce steering input signals proportional to thedesired inclination angle and azimuth angle. In the flex sectioncontroller 72, a desired inclination angle signal 90 is fed to acomparator 92 along with an inclination angle feedback signal 94 fromthe flex position transducer 54. This sensor detects positional changesfrom the flex section piston, as described above, and feeds that databack to the comparator 92 which periodically compares the feedbacksignal 94 with the desired inclination angle input signal 90 to producean inclination angle error signal 100. This error signal is fed to acontroller 102 which operates the flex section valve motor 98 for makinginclination angle adjustments.

[0042] In the rotary section control loop 74 a desired azimuth anglesignal 104 is fed to a comparator 106 along with a rotary positionfeedback signal 108 from the rotary position transducer 62. This sensordetects positional changes from the rotator section piston describedabove and feeds that position data back to the comparator 106 whichcompares the feedback signal 108 with the azimuth angle input signal 104to produce an error signal 114 for controlling azimuth. The error signal114 is fed to a controller 116 which controls operation of the rotaryvalve section motor 112 for making azimuth angle adjustments.

[0043] The flex position sensor 54, which is interior to the steeringtool, measures how much the flex shaft is deflected to provide theposition feedback information sent to the comparator. The rotaryposition sensor 62 measures how much the rotator piston is rotated. Thissensor is located on the rotator piston and includes a magnet whichmoves relative to the sensor to produce an analog output which is fedback to the comparator 106.

[0044] A packerfoot 118 is actuated to expand into the annulus and makecontact with the wall of the borehole in situations where changes ininclination angle and azimuth angle are made simultaneously. Thepackerfoot is described in more detail below. An alternative grippermechanism can be used to assist the rotary section. One of these is theFlextoe Packerfoot, which has a multiplicity of flexible members (toes)that are deflected onto the hole wall by different mechanisms, includinginflating a bladder, or lateral movement of a wedge-shaped element intothe toe. These are described in U.S. patent application Ser. No.09/453,996, incorporated herein by reference. These gripping elementsmay incorporate the use of a mandrel and splines that allow the gripperto remain in contact to the hole wall while the tool advances forward.Alternatively, the component can remain in contact with the hole walland be dragged forward by the weight of the system. The design option todrag or allow the tool to slide relative to the gripper depends upon theloads expected within the tool for the range of operating conditions ofazimuth and inclination angle change.

[0045]FIGS. 5 through 10 illustrate components of the flex section 26 ofthe steering tool. FIG. 5 is an external perspective view of the flexsection which includes an elongated, cylindrical, axially extendinghollow drive shaft 120 (also referred to herein as a flex shaft)extending the length of the flex section. The major components of theflex section are mounted to an aft section of the drive shaft and extendfor about three-fourths the length of the shaft 120. In the externalview of FIG. 5 the components include an elongated external skin 122mounted concentrically around the shaft. The flex section componentscontained within the outer skin are described below. Helical stabilizerblades 124 project outwardly from the skin for contact with the wall ofthe borehole. A threaded connection 126 at the forward end of the driveshaft is adapted for connection to the drill bit 28 or to drill collarsadjacent a drill bit. At the aft end of the flex section, a threadedconnection 128 is adapted for connection to the rotary section of thesteering tool.

[0046] The cross-sectional view of FIG. 6 shows the drive shaft 120running the length of the flex section, with a forward end section 130of the drive shaft projecting axially to the exterior of the flexsection components contained within the outer skin 122. This assembly ofparts comprises a deflection actuator which includes an elongateddeflection housing 132 extending along one side of the drive shaft, andan elongated deflection housing cap 134 extending along an opposite sideof the drive shaft. The deflection housing and the deflection housingcap surround the drive shaft. An elongated deflection piston 136 iscontained in the annulus between the drive shaft and the combineddeflection housing and deflection housing cap. A forward endhemispherical bearing 140 and an aft end hemispherical bearing 138 joincorresponding ends of the flex section components contained within theouter skin to the drive shaft. Alternatively, the hemispherical bearingon the aft end can be a constant velocity joint, either of commerciallyavailable type or specially designed.

[0047] The exploded perspective view of FIG. 7 illustrates internalcomponents of the flex section. The deflection housing 132 has anupwardly opening generally U-shaped configuration extending around butspaced from the flex shaft. The deflection housing cap 134 is joined tothe outer edges of the deflection housing to completely encompass theflex shaft 120 in an open space within the combined deflection housingand cap. The deflection piston 136 is mounted along the length of theflex shaft 120 to surround the flex shaft inside the deflection housing,but in some configurations may extend only over a portion of the length,and its cap. The deflection piston extends essentially the entire lengthof the portion of the flex shaft contained in the deflection housing. Aflat bottom surface of the deflection housing cap 132 joins to acooperating flat top surface extending along the length of thedeflection piston 136. FIG. 7 also shows one of two elongated seals 142which seal outer edges of the deflection piston 136 to correspondinginside walls of the deflection housing.

[0048] The cross-sectional view of FIG. 8 best illustrates how thecomponents of the flex section are assembled. The hollow flex shaft 120extends concentrically inside the outer skin 122 along a concentriclongitudinal axis of the flex section. The deflection piston 136surrounds the flex shaft in its entirety and is mounted on the flexshaft via an aligned cylindrical low-friction bearing 144. The U-shapeddeflection housing 132 surrounds a portion of the flex shaft 120 and itspiston 136, with flat outer walls of the piston bearing againstcorresponding flat inside walls of the U-shaped deflection housing. Thelongitudinal seals 142 seal opposite outer faces of the deflectionpiston to the inside walls of the deflection housing. The fixeddeflection housing is mounted to the inside of the skin via an elongatedlow-friction bearing 146. A mud passage line 148 is formed internallywithin the deflection housing cap adjacent the top of the deflectionpiston. Drilling fluid under pressure in the passage is applied as alarge pushing force to the top of the piston for deflecting the pistondownwardly into the deflection housing. The passage extends the lengthof the piston to distribute the hydraulic pushing force along the lengthof the piston. Alternatively, the deflection piston may be used over aportion of the flex shaft. Deflection of the piston is downwardly into avoid space 149 located internally below the piston and within theinterior of the deflection housing. Deflection of the piston 136 has theeffect of bending the flex shaft and thereby changing the angle ofinclination at the end of the shaft (also referred to herein as a flexshaft deflection angle). This deflection of the flex shaft adjusts theinclination angle of the drill bit at the end of the steering tool. Theregion between the outer skin and both the deflection housing and thedeflection housing cap has a low friction material that acts as abearing.

[0049] The relatively stiff deflection housing provides a structuralreaction point for the internal flex shaft. The internal supportstructure provides a means for allowing the flex shaft to react against.As mentioned, the deflection piston runs the length of the flex sectionand the pressure is applied to the top of the piston to displace theflex shaft. The amount of this displacement of the deflection piston isgreatest at its mid section between the hemispherical bearings at theends of the flex section. The space is provided to allow the deflectionpiston to move or deflect within the deflection housing and thisdeflection varies along the length of the tool and is greatest at themidpoint between the hemispherical end bearings.

[0050] The flex shaft 120 rotates within the deflection piston 136. Theregion between the deflection housing and the flex shaft has itshydraulic bearing 164 lubricated either by mud (if in an open systemwhich is preferred) or hydraulic oil (if sealed) and may include Teflonlow friction materials. Pressure delivered between the deflectionhousing and the deflection piston (through the line 148) moves both thedeflection piston and the flex shaft, while the flex shaft rotates withthe drill string.

[0051] The reaction points for the skin and deflection housing are themultiple stabilizers 124 located on the forward and aft ends of thetool, although in one configuration a third set of stabilizers islocated at the center, as shown in the drawings. The stabilizers may beeither fixed or similar to a non-rotating style hydraulic bearing. Thestabilizers cause the skin and the deflection housing to be relativelyrigid compared to the flex shaft.

[0052] In one embodiment, the deflection housing and deflection housingcap are both made from rigid materials such as steel. The flex shaft, inorder to facilitate bending, is made from a moderately high tensilestrength material such as copper beryllium.

[0053]FIGS. 9 and 10 show the aft and forward ends of the flex section,respectively, including the flex shaft 120, deflection piston,stabilizers 124, the outer skin 122 and the hemispherical bearings. FIG.9 shows the hemispherical bearing 138 at the aft end of the flexsection, and FIG. 10 shows the hemispherical bearing 140 at the forwardend of the flex section. The bearings used to support the flex shaft canbe various types, and preferably, the bearings rotate in a mannersimilar to a wrist joint. The hemispherical bearings shown can be sealedand lubricated or open to drilling fluid. The hemispherical bearings canbe limited in deflection to less than 15 degrees (from horizontal) ofdeflection. Alternatively, constant velocity joints can be used. RMZInc. of Sterling Heights, MI produce a constant velocity joint withsmooth uniform rotary motion with deflection capability up to 25degrees. CV joints are low cost and efficiently transfer torque but willrequire that sealing from the drilling fluid.

[0054] Control for the flex section may be located in either the flexsection or the rotary section but preferably in the rotary section.Again, the mud pulse telemetry is used to provide controls to thesteering tool. Mud pulses are sent down the bore of the drill string,received by the mud pulse telemetry section, and then commands are sentto the flex and rotary sections. The flex section's electrical controlsoperate the electrical motor in a pressure compensated environment whichcontrols the valve that delivers a desired drilling fluid pressure tothe deflection housing, producing a desired change in inclination. Theinclination angle changes produced by flexing the flex shaft andtransmitted to the steering tool are at the end of the flex shaft.

[0055] The transducer used to measure deflection of the flex shaft ordeflection housing provides feedback signals measuring the change ininclination of the tool as described previously. Other means ofmeasuring flex shaft deflection can be used. Different types ofdisplacement transducers can be used to determine the displacement ofthe shaft.

[0056] Significantly, because of this system design, the steering toolcan be operated to change either inclination or azimuth separately andincrementally, or inclination or azimuth continuously andsimultaneously, thus avoiding the downhole problem of differentialsticking.

[0057] The aft end of the deflection housing is equipped with teeth thatmesh into matching teeth in the rotary section. The joining of thedeflection housing to the rotary section allows the rotary section torotate the deflection housing to a prescribed location. The size andnumber of teeth can be varied depending upon tool size and expecteddeflection range of the flex section. The construction and operation ofthe rotary section is described as follows.

[0058]FIGS. 11 and 12 show external and longitudinal cross-section viewsof the rotary section 24 of the steering tool, in its alignment betweenthe flex shaft 120 and the mud pulse telemetry section 22. Thecross-sectional view of FIG. 12 shows a mud pulse telemetry housing 152concentrically aligned along the steering tool with the flex shaft 120and a rotary section housing 154. The housing 154 is joined to the mudpulse telemetry housing 152 and is also aligned concentrically with theflex shaft 120. FIGS. 13 to 16 show detailed cross-sectional views ofthe rotary section from the aft end to forward end of the steering tool.

[0059] Referring to FIG. 13, a tool joint coupling 156 connects to thedrill string and delivers rotary motion to the flex shaft 120. Athreaded end coupling 158 at the end of the flex shaft connects to thetool joint coupling 156. The tool joint coupling delivers rotary motionto the drive shaft and then through the hemispherical (or constantvelocity) bearings to the flex shaft, the end of which is connected tothe drill bit 28. A bearing pack 160 juxtaposed to the tool jointcoupling prevents rotation from being delivered to the mud pulsetelemetry housing 152 in response to rotation of the drill pipe and theflex shaft.

[0060] Referring to FIG. 14, the mud pulse telemetry housing 152contains the mud pulse telemetry transmitter, actuator/controller andsurvey electronics. The power supply 162 and steering tool electronics164 are schematically shown in FIG. 14. These components are containedwithin an atmospherically sealed environment. Electrical lines 166 feedthrough corresponding motor housings and house the electric motors forthe flex section control valve and the rotary section control valve. Theelectrical motors include the flex section valve motor 98 and the rotarysection motor 112. The electrical motors may be either DC stepper or DCbrushless type as manufactured by CDA Intercorp., Deerfield Beach, Fla.The motors are housed in a region containing hydraulic fluid, such asRoyco 756 oil, from Royco of Long Beach, Calif. Electrical connectors,such as those manufactured by Greene Tweede & Co., Houston, Tex.,connect the motors to the atmospheric chamber of the mud pulse telemetryelectronics. The hydraulic fluid surrounding the motors is separatedfrom the drilling fluid by a piston (not shown) for providing a pressurecompensated environment to ensure proper function of the motors atextreme subterranean depths. The electric motors are connected to eitherthe flex section control valve or to the rotary section control valvevia a Western Well Tool-designed motor cartridge assembly 172. Drillingfluid is delivered to either the rotary section valve or to the flexsection valve via fluid channels in each motor housing and valvehousing. The rotary section valve 56 is contained within a valve housing174 mounted in a recess in the rotary section. The rotary section valvecomprises a spool type valve with both the spool and the valve housingconstructed of tungsten carbide to provide long life. This rotarysection valve and its related components for applying rotational forceswhen making changes in azimuth angle are referred to herein as a rotatoractuator.

[0061] A filter/diffuser 173 is contained within the motor housing, anddrilling fluid passes through the drive shaft via a multiplicity ofholes and into the filter/diffuser. Drilling fluid from the flex sectionvalve 40 moves through flow passages through a valve housing 175 to thedeflection housing 132, thereby pressurizing the flex piston 136. Theflex valve housing is mounted in a recess in the rotary section oppositefrom the rotary valve housing. The flex section valve 40 is a spool typevalve made tungsten carbide. Fluid returning from the deflection housingis discharged to the annulus between the steering tool and the wall ofthe borehole.

[0062] Referring to FIGS. 15 and 16, drilling fluid from the rotarysection valve 40 passes via fluid flow passages 176 through the rotaryvalve housing 175 and into either side (as directed by the valve) of theregion of a rotary double-acting piston 178. Drilling fluid from theother side of the piston 178 returns via fluid passageways to the rotaryvalve 56 and is discharged to the annulus. Drilling fluid also passesthrough flow passages 176 via a pressure manifold 177 to the rotaryhousing and then to the deflection housing. The aft end of the rotarydouble-acting piston has splines 180 connected to a spline ring 182. Thesplines restrict motion of the rotary double-acting piston (and itsshaft) to strictly linear motion. The aft end of the rotarydouble-acting piston is sealed from the drilling fluid by a piston 184(referred to as valve housing to rotary section piston or VHTRS piston).The VHTRS piston includes piston seals 186, and this piston provides aphysical closure for the area between the valve housing and the rotarysection. As the rotary double-acting piston 178 moves forward linearly,its helical teeth engage matching helical grooves in the rotary housing154. The helical teeth or gears on the rotary double-acting piston areshown at 188 in FIG. 17. The rotary housing is connected via recessedteeth to the deflection housing and the deflection housing cap.Pressurized drilling fluid delivered to the rotary double-acting pistonresults in rotation of the deflection housing, thus changing thesteering tool's azimuth position.

[0063] The perspective view of FIG. 17 shows components of thethree-dimensional steering tool as described above to better illustratethe means of assembling them into an integrated unit.

[0064] The rotary section achieves changes in the azimuth by thefollowing method. At the surface, a signal is sent to the tool via themud pulse telemetry section. The mud pulse telemetry section receivesthe mud pulse, translates the pulse into electrical instructions andprovides an electrical signal to the 3-D control electronics.(Pressurization and actuation of the flex piston has been describedpreviously. Both the rotary and flex sections are pressurized andactuated simultaneously for the steering tool to produce both azimuthand inclinational changes.) The 3-D electrical controls provide anelectrical signal to either or both of the electric motors for therotary and the flex section valves. When the rotary valve is actuated,fluid from the bore passes through the filter and into the valve thatdelivers drilling fluid to the double-acting piston. The double-actingpiston is moved forward for driving the helical gears connected via acoupling to the deflection housing, which rotates relative to the flexshaft. The position of the double-acting piston allows positioning fromzero to 360 degrees in clockwise or counter-clockwise rotation, thuschanging the orientation of the deflection housing relative to the skin(which is resting on the hole wall thus providing a reaction point).Drilling fluid under pressure is delivered to the flex section andazimuthal change begins as follows. (Drilling fluid under pressure canbe applied via the method described to the reverse side of thedouble-acting piston to re-position the housing in a counter-clockwiseorientation.)

[0065] After the tool has drilled ahead enough to allow the drill stringto follow the achieved azimuth, the valve changes position, thedouble-acting piston receives drilling fluid, the flex piston isreturned to neutral, and straight drilling resumes.

[0066] The present invention can be applied to address a wide range ofdrilling conditions. The steering tool can be made to operate in alltypical hole sizes from 2-⅞ inch slim holes up to 30-inch holes, but isparticularly designed to operate in the 3-¾-inch up to 8-¾-inch holes.The tool length is variable, but typically is approximately 20 feet inlength. The tool joint coupling and threaded end of the flex shaft canhave any popular oil field equipment thread such as various AmericanPetroleum Institute (API) threads. Threaded joints can be made up withconventional drill tongs or similar equipment. The tool can withstand arange of weight on bit up to 60,000 pounds, depending upon tool size.The inside diameter of the drive shaft/flex shaft can be range from 0.75to 3.0 inches to accommodate drilling fluid flow rates from 75-650gallons per minute. The steering tool can operate at various drillingdepths from zero to 32,000 feet. The steering tool can operate over atypical operational range of differential pressure (the difference ofpressure from the ID of the steering tool to outside diameter of thetool) of about 600 to 3,500 PSID, but typically up to about 2,000 PSID.The size of the drive shaft/flex shaft can be adjusted to accommodate arange of drilling torque from 300 to 8,000 ft-lbs. depending upon toolsize. The steering tool has sufficient strength to survive impact loadsto 400,000 lbs. and continuous absolute overpull loads to 250,000 lbs.The tool's drive shaft can operate over the typical range of rotationalspeeds up to 300 rpm.

[0067] In addition, the rotary section and flex section require littledrilling fluid. Because the rotary section drilling fluid system is oflow volume, the operation of the rotary section requires from less than4 GPM to operate. The flex section is also a low volume system and canoperate on up to 2 GPM. Thus, the steering tool can perform its functionwith up to 6 GPM, which is from 1 to 5% of the total drilling fluidflowing through the tool.

[0068] For the rotary section, the velocity of the rotary double-actingpiston can range from 0.002 inches per minute to up to 8 inches perminute depending upon the size of the piston, flow channel size, andhelical gear speed.

[0069] The steering tool control section includes a helical screwposition sensor or potentiometer (not shown), as well as the previouslydescribed mud pulse telemetry actuator/controller electronics, surveyelectronics, 3-D control electronics, power supply, and transmitter.

[0070] One type of flex position transducer can be a MIDIM (mirror imagedifferential induction-amplitude magetometer). With this design, a smallmagnetic source is placed on the flex piston or the rotary double actingpiston and the MIDIM (manufactured by Dinsmore Instrument Company, 1814Remell St. Flint, Mich. 48503) within the body of the deflection housingor the rotary housing, respectively. As the magnetic source moves as aresult of the pressure on the piston, a calibrated analog outputprovides continuous reading of displacement. Other acceptabletransducers that use the method described above include a Hall effecttransducer and a fluxgate magnetometer, such as the ASIC magnetic sensoravailable from Precision Navigation Inc., Santa Rosa, Calif.

[0071] The mud pulse telemetry section provides the control informationto the surface. These systems are commercially available from suchcompanies as McAllister-Weatherford Ltd. of Canada and Geolink, LTD,Aberdeen, Scotland, UK as are several others. Typically these systemsare housed in 24 to 60-inch long, 2-⅞ to 6-{fraction (3/4)}-inch outsidediameter, 1 to 2 inch inside diameter packages.

[0072] Included in the telemetry section is a mud pulse transmitterassembly that generates a series of mud pulses to the surface. Thepulses are created by controlling the opening and closing of an internalvalve for allowing a small amount of drilling fluid volume to divertfrom the inside the drill string to the annulus of the borehole. Thebypassing process creates a small pressure loss drop in the standpipepressure (called negative mud pulse pressure telemetry). The transmitteralso contains a pressure switch that can detect whether the mud pumpsare switched on or off, thus allowing control of the tool.

[0073] The actuator/controller regulate the time between transmittervalve openings and the length of the pulse according to instructionsfrom the survey electronics. This process encodes downhole data to betransmitted to the surface. The sequence of the data can be specifiedfrom the surface by cycling the mud pumps in pre-determined patterns.

[0074] The power supply contains high capacity lithium thionyl chloridebatteries or similar long life temperature resistance batteries (oralternatively a downhole turbine and electrical generator powered bymud).

[0075] The survey electronics contain industry standard tri-axialmagnetometers and accelerometers for measuring inclination (zero to 180degrees), and azimuth (zero to 360 degrees) and tool face angle (zero to360 degrees). Tool face angle is the orientation of the tool relative tothe cross-section of the hole at the tool face. Included are typicallymicroprocessors linked to the transmitter switch that control toolfunctions such as on-off and survey data. Other types of sensors mayalso be placed in the assembly as optional equipment. These othersensors include resistivity sensors for geological formation informationor petroleum sensors.

[0076] The data are transmitted to the surface computer system (notshown). At the surface, a transmitter and receiver transmits andreceives mud pulses, converts mud pulses to electrical signals,discriminates signal from noise of transmissions, and with softwaregraphically and numerically presents information.

[0077] The surface system can comprise a multiplexed device thatprocesses the data from the downhole tool and also directs theinformation to and from the various peripheral hardware, such as thecomputer, graphics screen, and printer. Also included can be signalconditioning and intrinsic safety barrier protections for the standpipepressure transducer and rig floor display. The necessary software andother hardware are commercially available equipment.

[0078] Instructions from the mud pulse telemetry section are deliveredto the 3-D control electronics, (the electrical control and feedbackcircuits described in the block diagrams). The 3-D control electronicsreceive and transmit instructions to and from the actuator/controller toprovide communication and feedback to the surface. The 3-D steeringelectronics also communicate to the rotary position sensor and the flexposition sensor. A feedback circuit (as described in the block diagramof FIG. 4) provides position information to the 3-D steering toolelectronics.

[0079] Thus, changes in direction are sent from the surface to thesteering tool through the surface system, to the actuator/controller, tothe 3-D steering electronics, and to the electric motors of the rotaryand flex section valves that move either the flex piston or rotarydouble-acting piston. The new position of the piston is measured by thesensor, compared to the desired position, and corrected if necessary.Drilling continues with periodic positional measurements made by thesurvey electronics, sent to the actuator/controller to the transmitter,and then to the surface, where the operator can continue to steer thetool.

[0080] The electrical systems are designed to allow operation withindownhole pressures (up to 16,000 PSI). This is typically accomplishedwith atmospheric isolation of electrical components, specially designedelectrical connectors that operate in the drilling environments, andthermally hardened electronics and boards.

[0081] The steering tool can include an optional flex toe gripper whosepurpose is to ensure a fixed location of the tool to an azimuthorientation. When the flex toe is activated it grips the wall of theborehole for making changes in inclination and/or azimuth. The flex toedesign includes flex elements that are pinned at one end and slide onthe opposite end. Underneath the flex elements are inflatable bladdersthat are filled with drilling fluid when pressurized and collapse whendepressurized. Drilling fluid is delivered to the bladder via amotorized valve, typically the rotary valve described previously. Thevalve is controlled in a manner similar to the motorized valves for theflex section or rotary section via mud pulse telemetry or similar means.

[0082] The flex toe is optional depending upon the natural tendency forthe 3-D steering tool's skin not to rotate; it can be provided as anoption to resist minor twisting of the drill string and maintain aconstant reference for the tool motion.

[0083] In a similar manner to the flex toe, a packerfoot (shownschematically in FIG. 3) can be utilized in the steering tool as amechanism to provide a reaction point for the rotary section whensimultaneously changing inclination and azimuth while drilling. Thepackerfoot developed by Western Well Tool is described in U.S. Pat. No.6,003,606, the entire disclosure of which is incorporated herein byreference. The packerfoot can be either rigidly mounted or can beallowed to move on a mandrel. When connected to a mandrel the packerfootprovides resistance to rotation but without dragging the packerfoot overthe hole wall.

[0084] Specific types of materials are required for parts of thesteering tool. Specifically, the shaft and flex piston must be made oflong fatigue life material with a modulus lower than the skin andhousing. Suitable materials for the shaft and flex piston arecopper-beryllium alloys (Young's modulus of 19 Million PSI). The tool'sskin and housing can be various steel (Young's modulus of 29 Millionpsi) or similar material.

[0085] Specialized sealing materials may be required in someapplications. Numerous types of drilling fluids are used in drilling.Some of these, especially oil-based mud or Formate muds are particularlydamaging to some types of rubbers such as NBR, nitrile, and naturalrubbers. For these applications, use of specialized rubbers such astetraflourethylene/propylene elastomers provides greater life andreliability.

[0086] The tool operates by means of changes in inclination or bychanges of azimuth in separate movements, but not necessarily bothsimultaneously. Typical operation includes drilling ahead, telemetry tothe 3-D steering tool, and changes in the orientation of the drill bit,followed by change in the inclination of the bore hole. The amount ofstraight hole drilled before changes in inclination can be as short asthe length of the 3-D steering tool.

[0087] For azimuthal changes, drilling ahead continues (with noinclination), telemetry from the surface to the tool with instructionfor changes in azimuth, internal tool actions, followed by change in theazimuth of the bore hole.

[0088] Other instruments can be incorporated into the steering tool,such as Weight-on-Bit, Torque-on-Tool, bore pressure, or resistivity orother instrumentation.

What is claimed is:
 1. A three-dimensional steering tool for use indrilling a borehole in an underground formation in which an elongatedconduit extends from the surface through the borehole and in which thesteering tool is mounted on the conduit near a drill bit for drillingthe borehole, the steering tool comprising an integrated telemetrysection, rotary section and flex section aligned axially along thesteering tool for separately controlling inclination and azimuth anglesat the drill bit; in which the flex section includes an elongated driveshaft coupled to the drill bit and adapted to be rotatably driven forrotating the drill bit, the drive shaft being bendable laterally todefine a deflection angle thereof, and a deflection actuator coupled tothe drive shaft, the deflection actuator comprising a deflection housingsurrounding the drive shaft and having a longitudinal axis and anelongated deflection piston movable in the deflection housing forapplying a lateral bending force to the drive shaft for making changesin the deflection angle of the drive shaft which is transmitted to thedrill bit as an inclination angle steering adjustment; in which therotary section is coupled to the actuator and includes a rotatoractuator for transmitting a rotational force to the deflection actuatorto rotate the deflection piston to thereby change the rotational angleat which the lateral bending force is applied to the drive shaft whichis transmitted to the drill bit as an azimuth angle steering adjustment;and in which the telemetry section measures the inclination angle andthe azimuth angle during drilling and compares them with desiredinclination and azimuth angle information to produce inclination controlsignals for operating the deflection actuator to make steeringadjustments in the inclination angle and for separately producingazimuth control signals for operating the rotator actuator for makingsteering adjustments in the azimuth angle.
 2. Apparatus according toclaim 1 in which the conduit is an elongated rotary drill string. 3.Apparatus according to claim 1 in which the deflection actuatorcomprises an elongated deflection housing surrounding the drive shaft,and an elongated hydraulically operated piston in the deflection housingfor applying the bending force distributed lengthwise along the driveshaft for flexing the drive shaft laterally to produce said deflectionangle thereof to thereby change the inclination angle at the drill bit.4. Apparatus according to claim 3 in which the rotator actuator iscoupled to the deflection housing and includes a rotator piston movablein proportion to a desired change in the azimuth angle and a helicalgear arrangement on the deflection housing coupled to the rotator pistonand rotatable in response to piston travel to rotate the deflectionhousing to change the azimuth angle at the drill bit.
 5. Apparatusaccording to claim 1 in which the hydraulically powered bending force isapplied to the deflection piston by drilling mud taken from an annulusbetween the conduit and the borehole.
 6. Apparatus according to claim 1in which the deflection actuator applies the bending force to the driveshaft while the rotary actuator applies the rotational force to thedeflection actuator for making simultaneous adjustments in theinclination angles and the azimuth angles.
 7. Apparatus according toclaim 1 in which the feedback loop comprises a closed loop controllerincluding a comparator for receiving the measured and desiredinclination angle and azimuth angle command signals for producinginclination and azimuth error signals for making the steeringadjustments.
 8. Apparatus according to claim 1 in which the telemetrysection comprises an onboard mud pulse telemetry section for receivingthe desired inclination and azimuth angle input signals and utilizingmud pulse controls for operating the deflection actuator and the rotatoractuator from drilling mud taken from an annulus between the conduit andthe borehole.
 9. The apparatus according to claim 8 in which the mudpulse telemetry section provides open loop control to the deflectionactuator and the rotator actuator, and in which electrical controlsprovide closed loop control to the actuators.
 10. Apparatus according toclaim 1 in which the deflection actuator includes axially spaced-apartend bearings for mounting the drive shaft along a longitudinal axis ofthe steering tool, and a deflection piston for applying the lateralbending force to the drive shaft between the end bearings to bend thedrive shaft while the end bearings constrain the drive shaft on oppositesides of the deflection piston.
 11. Apparatus according to claim 1 inwhich the deflection piston contained in the deflection housing ispositioned on one side of the drive shaft and the drive shaft has alongitudinal axis aligned with a longitudinal axis of the deflectionhousing, and the lateral bending force is applied by the piston as aunitary force which physically bends the drive shaft to deflect itslongitudinal axis away from the axis of the deflection housing.